The Reliability of Passive Components for Automotive Designs

It’s not difficult to feel some empathy for basic passive components: those humble resistors, capacitors, and magnetics often get far less designer (and media) consideration compared to active devices such as processors, power-management ICs, discrete power devices, and RF components. They are expected to do one thing, do it well, and under difficult circumstances, while “stepping aside” to let those active devices shine through.

But system reliability necessitates that the numerous individual components work “to spec” across the whole operating spectrum of temperature, vibration, and even contaminants. Therefore, engineering and fabricating a reliable passive device which meets the arduous and stringent automotive-segment mandates is more complex than just paying modest attention to electrical and mechanical details, although those are very necessary steps.

How to Select Reliable Automotive Passive Components

For designers, there is more to choosing an automotive passive component than simply checking that it is “qualified.” They should ask, “Qualified for what?” There is no single minimum auto standard; instead, the industry has defined levels of ruggedness for the various settings within the vehicle, after all, the stress situation under the hood is different to the in-cabin environment.

The AEC (Automotive Electronics Council) is an industry organization that encourages the standardization of reliability or qualification standards for automotive electronic components; major automotive manufacturers and major electronic component manufacturers are amongst its members.

Qualification for automotive passives begins with the industry’s AEC-Q200 standard (note that the associated Q100 standard deals with ICs, while Q101 is for discrete semiconductors). There are five overall grades, with four spanning vehicle-use, from the relatively benign passenger compartment to the more hostile under-hood environment. Table:  

Although operating temperature range is a crucial ruggedness parameter called out by AEC-Q200, it is not the only one. Among numerous others described are temperature cycling, thermal stress, dimensional stability, terminal strength, solvent resistance, shock, vibration, solderability, flammability, and ESD.

These requirements must be accomplished while still meeting the basic electrical-performance specifications. In short, it’s not easy to get that “sticker” which proclaims, “Qualified to AEC-Q200, Grade Level x.”

Designers have two problems to manage because of this. Firstly, they must ensure that they do not “over specify” the passives on their BOM (Bill of Materials). There’s a monetary and even sourcing availability price involved with spec’ing Grade 1 (under-hood) when Grade 3 is acceptable.

There’s also the opposite concern of ensuring that the supply chain (purchasing, inventory, production) does not substitute a lower-performance grade for the specified one, whether due to human error, accessibility, or an ill-advised effort to save money.

When that sort of passive-component downgrade occurs, multiple consequences are possible - all unpleasant: unexpected field failures, finger-pointing (many times misguided and premature) often starting with the design team as to what went wrong and whose fault it was, the need for various forensic teams to do serious, time-intensive “detective” work with report writing and an action plan; perhaps even recalls and lawsuits (yes, these things happen…).

Conclusion

So, the lesson is clear: be diligent when considering the various levels and specifics of passive-components and their qualification. Select the correct one, work closely with your vendors, and be sure the design and qualification teams use it where and how it is intended.

This information has been sourced, reviewed and adapted from materials provided by TT Electronics plc.

For more information on this source, please visit TT Electronics plc.

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